[PATCH 14/15] x86/atomics: Remove !CONFIG_X86_CX8 methods

Ingo Molnar
2025-12-14T08:48:14Z

Cc: Ahmed S . Darwish <darwi@linutronix.de>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: H . Peter Anvin <hpa@zytor.com>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250425084216.3913608-16-mingo@kernel.org
---
arch/x86/include/asm/asm-prototypes.h | 4 -
arch/x86/include/asm/atomic64_32.h | 17 +--
arch/x86/include/asm/cmpxchg_32.h | 87 +--------------
arch/x86/lib/Makefile | 4 -
arch/x86/lib/atomic64_386_32.S | 195 ----------------------------------
arch/x86/lib/cmpxchg8b_emu.S | 97 -----------------
arch/x86/um/Makefile | 1 -
lib/atomic64_test.c | 7 +-
8 files changed, 8 insertions(+), 404 deletions(-)

diff --git a/arch/x86/include/asm/asm-prototypes.h b/arch/x86/include/asm/asm-prototypes.h
index 11c6fecc3ad7..6ec680a36dea 100644
--- a/arch/x86/include/asm/asm-prototypes.h
+++ b/arch/x86/include/asm/asm-prototypes.h
@@ -16,10 +16,6 @@
#include <asm/gsseg.h>
#include <asm/nospec-branch.h>

-#ifndef CONFIG_X86_CX8
-extern void cmpxchg8b_emu(void);
-#endif
-
#ifdef CONFIG_STACKPROTECTOR
extern unsigned long __ref_stack_chk_guard;
#endif
diff --git a/arch/x86/include/asm/atomic64_32.h b/arch/x86/include/asm/atomic64_32.h
index ab838205c1c6..1ac093b89c43 100644
--- a/arch/x86/include/asm/atomic64_32.h
+++ b/arch/x86/include/asm/atomic64_32.h
@@ -48,29 +48,14 @@ static __always_inline s64 arch_atomic64_read_nonatomic(const atomic64_t *v)
ATOMIC64_EXPORT(atomic64_##sym)
#endif

-#ifdef CONFIG_X86_CX8
#define __alternative_atomic64(f, g, out, in, clobbers...) \
asm volatile("call %c[func]" \
- : ALT_OUTPUT_SP(out) \
+ : ALT_OUTPUT_SP(out) \
: [func] "i" (atomic64_##g##_cx8) \
COMMA(in) \
: clobbers)

#define ATOMIC64_DECL(sym) ATOMIC64_DECL_ONE(sym##_cx8)
-#else
-#define __alternative_atomic64(f, g, out, in, clobbers...) \
- alternative_call(atomic64_##f##_386, atomic64_##g##_cx8, \
- X86_FEATURE_CX8, ASM_OUTPUT(out), \
- ASM_INPUT(in), clobbers)
-
-#define ATOMIC64_DECL(sym) ATOMIC64_DECL_ONE(sym##_cx8); \
- ATOMIC64_DECL_ONE(sym##_386)
-
-ATOMIC64_DECL_ONE(add_386);
-ATOMIC64_DECL_ONE(sub_386);
-ATOMIC64_DECL_ONE(inc_386);
-ATOMIC64_DECL_ONE(dec_386);
-#endif

#define alternative_atomic64(f, out, in, clobbers...) \
__alternative_atomic64(f, f, ASM_OUTPUT(out), ASM_INPUT(in), clobbers)
diff --git a/arch/x86/include/asm/cmpxchg_32.h b/arch/x86/include/asm/cmpxchg_32.h
index 1f80a62be969..840305da3fc6 100644
--- a/arch/x86/include/asm/cmpxchg_32.h
+++ b/arch/x86/include/asm/cmpxchg_32.h
@@ -68,88 +68,11 @@ static __always_inline bool __try_cmpxchg64_local(volatile u64 *ptr, u64 *oldp,
return __arch_try_cmpxchg64(ptr, oldp, new,);
}

-#ifdef CONFIG_X86_CX8
+#define arch_cmpxchg64 __cmpxchg64
+#define arch_cmpxchg64_local __cmpxchg64_local
+#define arch_try_cmpxchg64 __try_cmpxchg64
+#define arch_try_cmpxchg64_local __try_cmpxchg64_local

-#define arch_cmpxchg64 __cmpxchg64
-
-#define arch_cmpxchg64_local __cmpxchg64_local
-
-#define arch_try_cmpxchg64 __try_cmpxchg64
-
-#define arch_try_cmpxchg64_local __try_cmpxchg64_local
-
-#else
-
-/*
- * Building a kernel capable running on 80386 and 80486. It may be necessary
- * to simulate the cmpxchg8b on the 80386 and 80486 CPU.
- */
-
-#define __arch_cmpxchg64_emu(_ptr, _old, _new, _lock_loc, _lock) \
-({ \
- union __u64_halves o = { .full = (_old), }, \
- n = { .full = (_new), }; \
- \
- asm_inline volatile( \
- ALTERNATIVE(_lock_loc \
- "call cmpxchg8b_emu", \
- _lock "cmpxchg8b %a[ptr]", X86_FEATURE_CX8) \
- : ALT_OUTPUT_SP("+a" (o.low), "+d" (o.high)) \
- : "b" (n.low), "c" (n.high), \
- [ptr] "S" (_ptr) \
- : "memory"); \
- \
- o.full; \
-})
-
-static __always_inline u64 arch_cmpxchg64(volatile u64 *ptr, u64 old, u64 new)
-{
- return __arch_cmpxchg64_emu(ptr, old, new, LOCK_PREFIX_HERE, "lock ");
-}
-#define arch_cmpxchg64 arch_cmpxchg64
-
-static __always_inline u64 arch_cmpxchg64_local(volatile u64 *ptr, u64 old, u64 new)
-{
- return __arch_cmpxchg64_emu(ptr, old, new, ,);
-}
-#define arch_cmpxchg64_local arch_cmpxchg64_local
-
-#define __arch_try_cmpxchg64_emu(_ptr, _oldp, _new, _lock_loc, _lock) \
-({ \
- union __u64_halves o = { .full = *(_oldp), }, \
- n = { .full = (_new), }; \
- bool ret; \
- \
- asm_inline volatile( \
- ALTERNATIVE(_lock_loc \
- "call cmpxchg8b_emu", \
- _lock "cmpxchg8b %a[ptr]", X86_FEATURE_CX8) \
- : ALT_OUTPUT_SP("=@ccz" (ret), \
- "+a" (o.low), "+d" (o.high)) \
- : "b" (n.low), "c" (n.high), \
- [ptr] "S" (_ptr) \
- : "memory"); \
- \
- if (unlikely(!ret)) \
- *(_oldp) = o.full; \
- \
- likely(ret); \
-})
-
-static __always_inline bool arch_try_cmpxchg64(volatile u64 *ptr, u64 *oldp, u64 new)
-{
- return __arch_try_cmpxchg64_emu(ptr, oldp, new, LOCK_PREFIX_HERE, "lock ");
-}
-#define arch_try_cmpxchg64 arch_try_cmpxchg64
-
-static __always_inline bool arch_try_cmpxchg64_local(volatile u64 *ptr, u64 *oldp, u64 new)
-{
- return __arch_try_cmpxchg64_emu(ptr, oldp, new, ,);
-}
-#define arch_try_cmpxchg64_local arch_try_cmpxchg64_local
-
-#endif
-
-#define system_has_cmpxchg64() boot_cpu_has(X86_FEATURE_CX8)
+#define system_has_cmpxchg64() 1

#endif /* _ASM_X86_CMPXCHG_32_H */
diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index 2dba7f83ef97..210af275f468 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -48,10 +48,6 @@ ifeq ($(CONFIG_X86_32),y)
lib-y += strstr_32.o
lib-y += string_32.o
lib-y += memmove_32.o
- lib-y += cmpxchg8b_emu.o
-ifneq ($(CONFIG_X86_CX8),y)
- lib-y += atomic64_386_32.o
-endif
else
ifneq ($(CONFIG_GENERIC_CSUM),y)
lib-y += csum-partial_64.o csum-copy_64.o csum-wrappers_64.o
diff --git a/arch/x86/lib/atomic64_386_32.S b/arch/x86/lib/atomic64_386_32.S
deleted file mode 100644
index e768815e58ae..000000000000
--- a/arch/x86/lib/atomic64_386_32.S
+++ /dev/null
@@ -1,195 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-or-later */
-/*
- * atomic64_t for 386/486
- *
- * Copyright © 2010 Luca Barbieri
- */
-
-#include <linux/linkage.h>
-#include <asm/alternative.h>
-
-/* if you want SMP support, implement these with real spinlocks */
-.macro IRQ_SAVE reg
- pushfl
- cli
-.endm
-
-.macro IRQ_RESTORE reg
- popfl
-.endm
-
-#define BEGIN_IRQ_SAVE(op) \
-.macro endp; \
-SYM_FUNC_END(atomic64_##op##_386); \
-.purgem endp; \
-.endm; \
-SYM_FUNC_START(atomic64_##op##_386); \
- IRQ_SAVE v;
-
-#define ENDP endp
-
-#define RET_IRQ_RESTORE \
- IRQ_RESTORE v; \
- RET
-
-#define v %ecx
-BEGIN_IRQ_SAVE(read)
- movl (v), %eax
- movl 4(v), %edx
- RET_IRQ_RESTORE
-ENDP
-#undef v
-
-#define v %esi
-BEGIN_IRQ_SAVE(set)
- movl %ebx, (v)
- movl %ecx, 4(v)
- RET_IRQ_RESTORE
-ENDP
-#undef v
-
-#define v %esi
-BEGIN_IRQ_SAVE(xchg)
- movl (v), %eax
- movl 4(v), %edx
- movl %ebx, (v)
- movl %ecx, 4(v)
- RET_IRQ_RESTORE
-ENDP
-#undef v
-
-#define v %ecx
-BEGIN_IRQ_SAVE(add)
- addl %eax, (v)
- adcl %edx, 4(v)
- RET_IRQ_RESTORE
-ENDP
-#undef v
-
-#define v %ecx
-BEGIN_IRQ_SAVE(add_return)
- addl (v), %eax
- adcl 4(v), %edx
- movl %eax, (v)
- movl %edx, 4(v)
- RET_IRQ_RESTORE
-ENDP
-#undef v
-
-#define v %ecx
-BEGIN_IRQ_SAVE(sub)
- subl %eax, (v)
- sbbl %edx, 4(v)
- RET_IRQ_RESTORE
-ENDP
-#undef v
-
-#define v %ecx
-BEGIN_IRQ_SAVE(sub_return)
- negl %edx
- negl %eax
- sbbl $0, %edx
- addl (v), %eax
- adcl 4(v), %edx
- movl %eax, (v)
- movl %edx, 4(v)
- RET_IRQ_RESTORE
-ENDP
-#undef v
-
-#define v %esi
-BEGIN_IRQ_SAVE(inc)
- addl $1, (v)
- adcl $0, 4(v)
- RET_IRQ_RESTORE
-ENDP
-#undef v
-
-#define v %esi
-BEGIN_IRQ_SAVE(inc_return)
- movl (v), %eax
- movl 4(v), %edx
- addl $1, %eax
- adcl $0, %edx
- movl %eax, (v)
- movl %edx, 4(v)
- RET_IRQ_RESTORE
-ENDP
-#undef v
-
-#define v %esi
-BEGIN_IRQ_SAVE(dec)
- subl $1, (v)
- sbbl $0, 4(v)
- RET_IRQ_RESTORE
-ENDP
-#undef v
-
-#define v %esi
-BEGIN_IRQ_SAVE(dec_return)
- movl (v), %eax
- movl 4(v), %edx
- subl $1, %eax
- sbbl $0, %edx
- movl %eax, (v)
- movl %edx, 4(v)
- RET_IRQ_RESTORE
-ENDP
-#undef v
-
-#define v %esi
-BEGIN_IRQ_SAVE(add_unless)
- addl %eax, %ecx
- adcl %edx, %edi
- addl (v), %eax
- adcl 4(v), %edx
- cmpl %eax, %ecx
- je 3f
-1:
- movl %eax, (v)
- movl %edx, 4(v)
- movl $1, %eax
-2:
- RET_IRQ_RESTORE
-3:
- cmpl %edx, %edi
- jne 1b
- xorl %eax, %eax
- jmp 2b
-ENDP
-#undef v
-
-#define v %esi
-BEGIN_IRQ_SAVE(inc_not_zero)
- movl (v), %eax
- movl 4(v), %edx
- testl %eax, %eax
- je 3f
-1:
- addl $1, %eax
- adcl $0, %edx
- movl %eax, (v)
- movl %edx, 4(v)
- movl $1, %eax
-2:
- RET_IRQ_RESTORE
-3:
- testl %edx, %edx
- jne 1b
- jmp 2b
-ENDP
-#undef v
-
-#define v %esi
-BEGIN_IRQ_SAVE(dec_if_positive)
- movl (v), %eax
- movl 4(v), %edx
- subl $1, %eax
- sbbl $0, %edx
- js 1f
- movl %eax, (v)
- movl %edx, 4(v)
-1:
- RET_IRQ_RESTORE
-ENDP
-#undef v
diff --git a/arch/x86/lib/cmpxchg8b_emu.S b/arch/x86/lib/cmpxchg8b_emu.S
deleted file mode 100644
index d4bb24347ff8..000000000000
--- a/arch/x86/lib/cmpxchg8b_emu.S
+++ /dev/null
@@ -1,97 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-only */
-
-#include <linux/export.h>
-#include <linux/linkage.h>
-#include <asm/percpu.h>
-#include <asm/processor-flags.h>
-
-.text
-
-#ifndef CONFIG_X86_CX8
-
-/*
- * Emulate 'cmpxchg8b (%esi)' on UP
- *
- * Inputs:
- * %esi : memory location to compare
- * %eax : low 32 bits of old value
- * %edx : high 32 bits of old value
- * %ebx : low 32 bits of new value
- * %ecx : high 32 bits of new value
- */
-SYM_FUNC_START(cmpxchg8b_emu)
-
- pushfl
- cli
-
- cmpl (%esi), %eax
- jne .Lnot_same
- cmpl 4(%esi), %edx
- jne .Lnot_same
-
- movl %ebx, (%esi)
- movl %ecx, 4(%esi)
-
- orl $X86_EFLAGS_ZF, (%esp)
-
- popfl
- RET
-
-.Lnot_same:
- movl (%esi), %eax
- movl 4(%esi), %edx
-
- andl $(~X86_EFLAGS_ZF), (%esp)
-
- popfl
- RET
-
-SYM_FUNC_END(cmpxchg8b_emu)
-EXPORT_SYMBOL(cmpxchg8b_emu)
-
-#endif
-
-#ifndef CONFIG_UML
-
-/*
- * Emulate 'cmpxchg8b %fs:(%rsi)'
- *
- * Inputs:
- * %esi : memory location to compare
- * %eax : low 32 bits of old value
- * %edx : high 32 bits of old value
- * %ebx : low 32 bits of new value
- * %ecx : high 32 bits of new value
- *
- * Notably this is not LOCK prefixed and is not safe against NMIs
- */
-SYM_FUNC_START(this_cpu_cmpxchg8b_emu)
-
- pushfl
- cli
-
- cmpl __percpu (%esi), %eax
- jne .Lnot_same2
- cmpl __percpu 4(%esi), %edx
- jne .Lnot_same2
-
- movl %ebx, __percpu (%esi)
- movl %ecx, __percpu 4(%esi)
-
- orl $X86_EFLAGS_ZF, (%esp)
-
- popfl
- RET
-
-.Lnot_same2:
- movl __percpu (%esi), %eax
- movl __percpu 4(%esi), %edx
-
- andl $(~X86_EFLAGS_ZF), (%esp)
-
- popfl
- RET
-
-SYM_FUNC_END(this_cpu_cmpxchg8b_emu)
-
-#endif
diff --git a/arch/x86/um/Makefile b/arch/x86/um/Makefile
index f9ea75bf43ac..2513aca5156a 100644
--- a/arch/x86/um/Makefile
+++ b/arch/x86/um/Makefile
@@ -20,7 +20,6 @@ ifeq ($(CONFIG_X86_32),y)
obj-y += syscalls_32.o

subarch-y = ../lib/string_32.o ../lib/atomic64_32.o ../lib/atomic64_cx8_32.o
-subarch-y += ../lib/cmpxchg8b_emu.o ../lib/atomic64_386_32.o
subarch-y += ../lib/checksum_32.o
subarch-y += ../kernel/sys_ia32.o

diff --git a/lib/atomic64_test.c b/lib/atomic64_test.c
index d726068358c7..d7697c09041f 100644
--- a/lib/atomic64_test.c
+++ b/lib/atomic64_test.c
@@ -251,15 +251,12 @@ static __init int test_atomics_init(void)
test_atomic64();

#ifdef CONFIG_X86
- pr_info("passed for %s platform %s CX8 and %s SSE\n",
+ pr_info("passed for %s platform with CX8 and %s SSE\n",
#ifdef CONFIG_X86_64
"x86-64",
-#elif defined(CONFIG_X86_CX8)
- "i586+",
#else
- "i386+",
+ "i586+",
#endif
- boot_cpu_has(X86_FEATURE_CX8) ? "with" : "without",
boot_cpu_has(X86_FEATURE_XMM) ? "with" : "without");
#else
pr_info("passed\n");
--
2.51.0